Multitank Heat Storage

This three tank system demonstrates the value of a multi tank heat storage vault.

HEAT INPUT
Tank 1 will always be the warmest because it is the first to exchange heat coming from the collector. The second tank is heated in a like manner though it will never get as hot as the first. Tank 2 is the warmer tank. Tank 3 is designed to suck the last bit of heat from the already cooled collector fluid. This warm tank will always be the coldest of the three tanks. Fluid returned from this tank will be nice and cold and ready for efficient heat transfer when it’s returned to the hot collector.

HEAT OUTPUT

Cold well water flows through tubes near the tops of the tanks where storage tank water is hottest. Well water is heated in three successive stages. Tank 3 preheats well water for tank 2 and tank 2 preheats the water for tank 1, the warmest tank.
Multi tank heat storage systems maximize heat transfer efficiency.
Notice that the collector fluid heat exchange coils are located near the bottom of the tank. Do you think this is a good idea? Why or why not?
Domestic heat exchange tubes are located near the top of the tank. Do you think this is a good arrangement? Why or why not?

If sufficient storage tanks and sufficient collectors are used fossil fuel heating would be unnecessary. For a slide show demonstrating the construction details of a multi tank heat storage system for home heating click here: Multi Drum Heat Storage Vault

You may need some plumbing assistance to build this multi tank heat storage vault. 

MATERIALS FOR A 1' X 3' X 1' MULTI TANK HEAT STORAGE VAULT

1. Three 10' lengths of 1/2 inch copper tubing.
2. Sixteen 1/2 inch elbows, four T's solder etc.
3. Two 1x12x8's, one 2x2x8
4. 60lb Mortar mix
5. Three small (13 cu ft) garbage bags

HEAT INPUT PLUMBING

First cut a three foot length from a 1x12. This will be the bottom of the heat input exchange system. Then attach the 2x2 frame to this as shown in the picture.
Cut four pieces of copper tubing 40" long and then drill four 3/4 inch holes 2" apart into the ends of the 2x2's.
Insert these 40" long copper tubes into the 2x2's.
Next sweat the copper tubes together with elbows and T's as shown in the picture.

After the plumbing is done pour cement into the 2x2 frame and be sure make it level with the top of this frame. Congratulations! You have just constructed the heat sink for the heat input system.

HEAT STORAGE VAULT

Now let's build the heat storage vault.
First cut two 11" pieces of 1x12 and round off the edges as shown in this picture. These will be the tank barriers and they will be exposed to water so they should be protected with oil paint.

 

Cut two end pieces 1 x 12 x 1'
Cut two side pieces 46.5 inches. These side pieces will have 1/2" deep notches  3/4" wide centered one foot from both ends of the board. Examine the following picture to see the position of the notches.  

After cutting and shaping and sanding these notches you can assemble the heat storage vault with screws. Make sure that the tank barriers fit loosely and are well sanded before continuing.

Cut notches 3/4" wide and 2" deep into the tops of the tank barriers. These notches should be centered and spaced about 2" apart. Sand all rough edges, remove the tank barriers and paint the assembly with oil base paint.

After the assembly is dry line the inside of the vault with a few sheets of plastic to make it waterproof.

HEAT OUTPUT PLUMBING

Insert the tank barriers with notches cut into the top. 

Now assemble the heat output plumbing as shown in this picture.
Cut four 1/2 inch copper tubes 30" long. 

After assembling  the elbows and T's so that the 30" lengths of copper tubing are spaced about 2" apart remove the assembly and sweat the joints away from the heat storage vault. Remember the heat storage vault is now lined with plastic. 

Cross supports hold the heat storage vault together, and also hold the tank barriers down.

For large tanks solid Styrofoam insulation is used. Can you imagine the buoyancy force of ultra light insulation under six feet of water?

Without cross supports solid insulation tank barrier walls would pop out of the tank as soon as water is added.

Best of luck with this project. it's a good one.

Isolating the heat storage area from the heat collection area is important since solar energy is intermittent.
Collectors should be both large and inexpensive to be practical. The absorber plate should make intimate contact with flow tubes in as many places as possible. This is why pre-bending aluminum absorber plates to fit the contour of the copper is so important. Pre-bending the aluminum could easily increase the heat transfer process by more than 1000 %.

I no longer use metal flow tubes or metal absorber plates in my collector designs but if you are adamant about using this method of transferring heat consider the merits of building a bending jig to facilitate the fabrication of a more efficient absorber plate.